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Questions tagged [log-amplifier]

Logarithmic amplifier ("Log Amp").

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Fine tuning of anti-log op-amp for LED driving

I have a 10-bit DAC that outputs a voltage between 0 and 3V. This signal controls a current-driver for LEDs. I need to compensate the "log" behavior of the LEDs, otherwise the first steps ...
Mark's user avatar
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3 votes
1 answer
120 views

Simulation of log configuration for op-amp

I'm quite new to pspice and I'm trying to simulate the dc transfer function of an op-amp in log configuration. Here my circuit. I'm using Kicad and ngspice: R3 and R4 are there because it gave me ...
Mark's user avatar
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4 votes
2 answers
255 views

Can I compress the dynamic range of ns pulses to better fit ADC range using log amp or mixer?

I have an experiment in which the signal I want to measure is a 1 ns pulse that occurs somewhere around 0-100 ns after a trigger. I want to digitize the pulses to extract the time they occurred and ...
argentum2f's user avatar
1 vote
1 answer
205 views

Multiplier and divisor using logarithmic and anti-logarithmic op-amps, issue with output

I was tasked to make 4 processes using operational amplifiers: adding, substraction, multiplication, and division. However, only the add and substract operations work: whenever I try to multiplicate ...
JCorona98's user avatar
0 votes
3 answers
651 views

Simulating voltage divider?

Over the past weeks, I've been looking into an analog method of dividing 2 voltages such that V1/V2=Vout. I found many sources on Google using methods like log and antilog amplifiers or a multiplier, ...
Wrig Nine's user avatar
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2 answers
4k views

Op-Amp Based Multiplier LTSpice Simulation

I'm supposed to make a multiplier with log amplifier configuration using LM741 op-amps and 1N4001 diodes. I found this circuit configuration in this Youtube video. However, the output voltages I get ...
Boffin's user avatar
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0 votes
2 answers
263 views

Is this IC damaged or fake?

I am trying to test a AD8307. Here are my connections: (pins not shown are left unconnected, and also pin 8). I get a quiescent output voltage at pin 4 of about 850 mV with respect to ground, which, ...
MikeTeX's user avatar
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3 votes
4 answers
514 views

Why does my diode log amplifier in LTspice not match theory?

I am trying to learn about analog multipliers, and I'm trying to implement one using a log-antilog design. I am currently having some difficulties with the log part because simulating an ideal ...
Paolo Celati's user avatar
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1 answer
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Does a wide-band, high-current, inline ammeter circuit already exist?

I have an application where I would like to measure currents up to 1000 A, inline, but am also interested in using the same circuit for a low current part of the cycle. The thought is that if I can ...
J Collins's user avatar
  • 585
0 votes
3 answers
448 views

replacing AN6878 led driver IC

I'm trying to replace the obsolete AN6878 led driver (logarithmic response, used for audio level indicator) with a modern and available solution. I'd like to keep the same functionality of the ...
Dimitri Petrucci's user avatar
4 votes
1 answer
200 views

Logarithmic amplifier with high slew rate -- mutually exclusive?

Does anyone know if the basic construction of a log amp (with a diode or BJT providing feedback from output to input) is in conflict with any ability to reach high slew rates? I've been looking (...
stevegt's user avatar
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1 vote
3 answers
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Analog multiplier using logarithmic and anti-logarithmic opamp output problem

I'm trying to build a analog multiplier that takes in two voltages and produces the product of them. I have tried to simulate a circuit. Simulation with this methods is part of the objectives in the ...
Maulana Falithurrahman's user avatar
0 votes
2 answers
386 views

Why are all log amp examples with common base logging transistors?

I am not experienced with log amps, and am trying to learn about them. Every log amp article has the base of the logging transistor grounded. simulate this circuit – Schematic created using ...
DavidG25's user avatar
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2 votes
4 answers
307 views

Opamp detection of extremely tiny voltage

I am working on a project that requires measuring absorbance of a solution. The circuit consist of an emitter led, a photodiode attached to an opamp with \$10^7\$ gain (TIA). The solution absorbs ...
Totally New's user avatar
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2 answers
2k views

How to convert exponential output to linear output

I have a sensor which gives me roughly exponential output from 0 to 6 volts. How would I convert this to a linear range?
mckryall's user avatar
1 vote
2 answers
912 views

Sound pressure to db analog

I'm trying to convert an amplified microphone output (it is from 0-5v, biased at 2.5v) to a linear response that correlates with db SPL. From my research, the output of the microphone directly ...
Warrick's user avatar
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2 votes
2 answers
428 views

Resistor on pin 3 of a Log Amplifier

I'm trying to understand what's the function or R2 resistor in this transdiode log amp configuration. I suppose I've to match the right value to give in order to minimize the effect of input bias ...
Brontolo's user avatar
4 votes
2 answers
749 views

Log amplifier with vacuum tubes

Is there a way to build a log amplifier using vacuum tubes? I would like to have a VU meter (with the proper log response,) but do not want to use solid state components. The output would be to an IN-...
Pentium100's user avatar
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4 votes
1 answer
1k views

How to increase max input current of logarithmic amplifier 10x-100x safely?

Is it possible to increase max allowed current of logarithmic amplifier to say 1A by some workaround without loosing capabilities in lower range: 0..1ma ? For example the TI part LOG112 has few ...
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29 votes
10 answers
24k views

LM394 is obsolete. What is the new standard log amp circuit?

The traditional logarithmic amplifier circuit is described in National Appnote 311: This circuit uses the difference of two transistor currents to generate the log of the input over a pretty wide ...
markrages's user avatar
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